W2 L4a - Evolving on Land: The Amniotes Flashcards
What are the 4 phylogenetically distinct groups in the Amniotes?
- Synapsida (Mammals & Mammal-like reptiles)
- Testudines (Turtles)
- Archosauromprha (Crocodiles, Dinosaurs, & Birds)
- Lepidosauromorpha (Lizards and Snakes)
What is a clade?
A group consisting of a single common ancestor and all it’s descendants
What does the cladogram of extant tetrapods look like?
—————————————— Amphibians
Synapsids
Turtles A
Turtles B
Sphenodon
Lizards
Snakes
Crocodiles
Birds
- Synapsids and under are Amniotes *
** Turtles and under are Sauropsids **
When did Amniotes evolve on land?
Around mid-Carboniferous (major radiation in Permian)
What are the defining features of Amniotes?
- Waterproof integument (skin) ➡ reduced or no respiration
- Developed lungs ➡ for respiration
- Increasing complexity of the heart
- Skeletal and skull changes ➡ locomotion and foraging
- Muscle changes in head and body ➡ locomotion and foraging
- Amniotic eggs ➡ **Most Important feature separating amphibians from all other Terrestrial vertebrates (Amniotes)
What is the Amniotic Egg?
- cleido = Greek “closed”
- Contains Amniotic fluid, Embryo, Yolk Sac, etc.
Amniotic Egg: Shell Features
- Leathery or calcified shell **still subject to desiccation
- Structural support in air
- Allows gas exchange ➡ H2O, O2, CO2
- Survival in drier areas
- Size ➡ direct development
- bypass larval stages; no gills
- larger (fewer, higher surv.) offspring - Internal Fertilization
Amniotic Egg: Yolk Features
- Nutrients; fuel
- ALL vertebrates have extra embryonic membranes enclosing yolk
** i.e. not unique to amniotes
Amniotic Egg: Unique Components
- Chorion: outer membrane for gas exchange
Allantois, Amnion, Yolk sac all inside Chorion - Allantois: “bladder” that stores nitrogenous waste
- Amnion: inner membrane providing cushion against mechanical shock
Amniotes split into what 2 major groups?
- Synapsids and Sauropsids
What are the specialized characteristics that differ in Synapsids and Sauropsids?
- Locomotor systems compatible with higher rates of lung ventilation
2.Reduced lateral undulations ➡ leg positioning
- Respiratory and excretory systems to conserve H2O
- Ecto- ➡ Endothermy
Describe the lung ventilation and locomotion in Amniotes
Sprawling Gait: conflict between running and breathing, to combat this:
- Locomotion & Respiration separated: for higher rates of lung ventilation - Reduced Lateral Undulations: changes in leg positioning - Respiratory and Circulatory systems changed
How do the brain structures differ in Synapsids vs Sauropsids?
Synapsids: good olfaction (smell), poor vision
Sauropsids: good vision, poor olfaction
- Specialize in diurnal activity
What is diurnal activity?
Active during the day, sleep at night
What is one of the main differences between Synapsids and Sauropsids?
The skull; separated by differences in the “temporal fenestration”
How do the anapsid, synapsid, and diapsid skulls differ between each other?
Anapsid: no fenestra between the postorbital and squamosal bone
Synapsid: one fenestra between the postorbital and squamosal bone
Diapsid: two fenestras between the postorbital and squamosal bone
Why did the skull evolution provide for the Amniotes?
Increased complexity of jaw musculature and feeding; snapping vs chewing
Which skulls belong to existing tetrapods?
Anapsid: Amphibians
Synapsid: Synapsids and Turtles A
Diapsid: Turtles B, Sphenodon, Lizards, Snakes, Crocodiles and Birds
Anapsid Skull Information
- Ancestral reptile condition
- No fenestras; sometimes a notch at the back
- Limits bite force
Diapsid Skull Information
- Two fenestras
- Attachment of larger, stronger jaw muscles; jaw can open much wider
- Allows animals to evolve away from “inertial snapping” (fish)
- Allows evolution of different types of teeth for different needs
- e.g. herbivore cropping/chewing vs carnivore tearing/shearing
What orders make up the Sauropsids (Class Reptilia)?
- Testudines (Turtles)
- Lepidosauromorpha (Lizards and Snakes)
- Archosauromorpha (Crocodiles and Birds)
When did the Sauropsids rise in evolution?
During the Permian-Triassic Extinction; ca. 250 mya
- largest Extinction event ever - generated the Mesozoic ➡ Age of the Reptiles
What are the Sauropsids defining features?
- Respiration
- Circulation
- Metabolism/-thermy
- Nitrogenous wastes
- Hearing
- Vision
- Olfaction
- Foraging
- Locomotion
- Reproduction
- Predator avoidance
- Adaptations to extreme conditions
Is breathing on land easier than the ocean?
Yes,
- air has a higher oxygen content
- need less volume to meet metabolic demands
- air less dense and less viscous
- can pump easily over respiratory surfaces
How did Sauropsids adapt to breathe on land?
The Aspiration Pump
How does the Aspiration Pump work?
- Negative pressure aspiration pump
- Rib cage expanded using ribs or muscles to create negative pressure in the abdominal cavity; sucks air into the lungs
- Complex subdivisions to increase surface area for gas exchange
What allows air to flow through the nostrils into the mouth cavity in Sauropsids?
A palate
How did the palate evolve to aid Sauropsids in respiration?
The partial palate in reptiles evolved to full secondary ones in Mammals and Birds
- Separates nostrils from the mouth; allowing them to eat and breath at the same time
What did Sauropsids have to overcome on land for circulation purposes?
Gravity, blood pooling at extremities, blood has to be pumped using high pressure
However, gas exchange in lungs requires a low flow rate and pressure to allow diffusion of oxygen
How does circulation work in Amniotes?
Amphibians:
- double-circuit
- 3 chambers
- incomplete separation of flow to lungs and skin
“Reptiles” (Turtles, Snakes, Lizards):
- double-circuit
- 3 chambers
- nearly complete separation of flow to lungs and body
How did these adaptations in circulation aid Amniotes on land?
Breathing air; due to the two separate blood flow circuits
- Systemic: transports oxygenated blood to the body (and back to the heart) - Pulmonary: transports deoxygenated blood to the lungs (and back to the heart)
How did evolving to Ectothermy aid the Sauropsids on land?
Regulated their body temperature from external sources, e.g. the sun
The mechanisms of ectothermic thermoregulation can be behavioral or physiological
